AN ASPECT OF SEQUENCE STRATIGRAPHIC STUDIES IN BORNU BASIN USING GAIBU – 1 WELL

Abstract

Two hundred and ten (210) ditch cutting samples obtained within the depth range of 1500 to 4600 m in Gaibu -1 well from the Bornu Basin were subjected to sedimentologic, palynological, foraminifera and calcareous nannofossil as well as electrofacies studies. The aim was to establish the age, paleoenvironment and subsequently sequence stratigraphic analysis in the basin using standard procedures in biostratigraphic studies and PetrelTM software. Sedimentological studies enabled a sub-division of the sequences penetrated by the well into six lithostratigraphic units composed of mainly silliciclastic rocks consisting of alternation of sand/sandstone, shale, shaly – sand and sandy – shale occasionally with subordinate calcareous materials. Only one planktic foraminiferal zone Globotruncanita elevata - Globotruncana aegyptiaca Zone indicating Early Campanian to late Maastrichtian sequences could be identified in this study due to rare occurrence of planktics in the well. Due to rare nannofossils occurrence Micula concava – Watznueria barnesae (CC16-Younger) Zone could be established in the well. However, four palynozone A(1) – A(4) with age , ranging from Cenomanian to Maastrichtian (?Younger) were established. Nine depositional sequences were recognized based on the palynozones, microfauna abundance and diversity patterns as well as the stacking patterns derived from wireline log of the well. The environment of deposition of the sequences penetrated by the well ranges from continental through shallow marine to open marine. High resistivity log recorded within some sand beds within the well suggests hydrocarbon occurrence in the basin.